During well operations, “matrix acidizing” and “acid fracturing” methods are employed to enhance the productivity of hydrocarbon wells. In general, acid or acid-based fluids are injected into the well tubing (the “injection phase”) and into the formation rock. These acids dissolve or partially dissolve the formation rock, creating alternative flow paths for hydrocarbons. After the acids are “spent” in the formation rock, they are returned to the surface through the same well tubing during the “flowback phase”.
One of the difficulties encountered when acid-based fracturing methods are employed is that most of the well tubing and downhole equipment is made of metal. In traditional acid-based fracturing methods utilized in oil wells, particularly as temperatures and pressures increase, the injected acids are corrosive to the metal tubing and the downhole equipment. To help prevent this, corrosion inhibitors are typically added to the acids. The corrosion inhibitors act to coat the metal and minimize the corrosive effects of the acids. As temperatures and pressures increase, acid reactivity also increases and increased amounts of inhibitor are needed to compensate for the increased reactivity.
Another difficulty encountered in typical acid-based fracturing methods is that after the acid is “spent”—injected into the formation rock for acid fracturing purposes—the acid still retains corrosive properties that will damage metal on its return to the surface during the “flowback phase”. Most prior art corrosion inhibitors work by coating the metal tubing during the “injection phase,” and the inhibitors typically are then consumed during this phase of the operation. After the acids have passed through the formation rock, little to no inhibition content is available to protect the well equipment during the “flowback phase” of the operation.
The cost of corrosion inhibitors in acid-based operations is a major contributor to the overall cost of the fracturing operation. Because of their corrosive properties, the most effective acids for fracturing require inhibitor dosages that lie outside of economic feasibility. Additionally, the “spent acids” can damage the well equipment during the “flowback phase”. Therefore, it would be advantageous to use a composition capable of protecting the well equipment, including pipes, electric submersible pumps (ESPs), and other downhole tools, in both the injection and flowback phases.